A compelling central performance from Bryan Cranston, ably supported by an excellent ensemble cast, featuring sterling work from Helen Mirren, Diane Lane, Louis CK, and Elle Fanning in particular, is not enough to save Trumbo from being rather a mess.

The film is poorly paced, something of a serious flaw in a movie that has to be profoundly rooted in its chronology, and it never seems to decide what it wants its register to be.

At times it appears to want to be a serious socio-political history, making weighty comments on a dark moment in America's past: Cranston's Dalton Trumbo, a successful Hollywood screenwriter blacklisted for his support for the Communist Party, talks weightily of the blacklist's "horror, its cruelty, its hideous waste of life", but we never really get a sense of that. In fact, there's a knockabout, caper-movie feel to whole segments; the sequence where Trumbo enlists his children into a kind of cottage industry of B-movie script production under a roster of false names was snappy and funny, but didn't seem in keeping with the film's apparent attempts to communicate something weighty and meaningful.

There's no rule that says films about heavy subjects have to be heavy in tone, but Trumbo feels like it keeps trying to remind us how meaningful it is, before immediately undermining itself. If the effect is deliberate, it was lost on me; for me, it rendered the film simply messy.

This feels like a missed opportunity to tell an important story, a minimising of the historical material it portrays. The film's central subject matter, the blacklisting of film workers, most prominently screenwriters, who were associated with the Communist Party of the USA, is rendered almost as an interpersonal squabble, even a kind of genteel duel of wits, between Hollywood glitterati. The only sense we get that any of these people were acting out of sincere political conviction, and that they wanted to change the world rather than simply win Oscars, is communicated in a few throwaway lines from Louis CK's Arlen Hird, a fictionalised composite of the more politically hardcore members of Trumbo's milieu. Louis CK portrays him brilliantly but disappointingly as a kind of world-weary, beaten-down schlub who lacks Trumbo's pizazz.

It might perhaps be argued that the movie is a biopic, not a social history, so it's right that the focus is on Trumbo and his relationships rather than wider politics. It is based on Bruce Cook's biography of Trumbo, which I must confess to not having read. It leaves us with an impression of Dalton Trumbo as a clever, talented man who certainly made personal sacrifices to win the right to openly pursue his art — but little more than this. Beyond one scene, very early on in the film, where he addresses a picket line of striking set workers, we do not get a sense of him as a participant in any wider struggle other than his own and that of his immediate colleagues. It's difficult to disagree with the detractor who snidely refers to him as a "swimming pool Soviet".

That is probably unfair to Trumbo. It is almost certainly unfair to others of the Hollywood 10, and certainly to many of the other victims of the blacklist. These people, who suffered greatly at the hands of a repressive and paranoid political class, deserve to be taken seriously as political actors (no pun intended) in their own right. They were not simply unaffiliated dissidents, they were members and supporters of the Communist Party of the USA. The actual politics of the Communist Party are never discussed; we only get a two line intro that tells us many people joined the CPUSA in response to fascism and the Great Depression.

The value system of the film is sincere liberalism; it wants us, rightly, to side with those blacklisted, out of a basic commitment to decent, liberal-democratic values. It would frightfully complicate the picture to admit the uncomfortable fact that the regime the CPUSA supported, and was an American satellite of, was busy brutally crushing decent, liberal-democratic values across large swathes of the world.

The blacklisted workers were victims of illiberal, anti-democratic repression. Many of them were also, despite their undoubtedly sincere intentions, supporters of the repression being carried out by "their", Stalinist, side. By both minimising the seriousness of US repression, and sidelining the politics of the matter, Trumbo misses an opportunity. It entertains, but does not educate much beyond a superficial level. No work of art has an inherent duty to do so, but this film seems to repeatedly try to tell us that it wants to, and on that score one must conclude that it fails.